This invention relates to water evaporation retardation and, more particularly, to improving the spreadability of evaporation retarding agents.
My U.S. Pat. No. 3,531,239, which issued on Sept. 29, 1970, discloses a method for forming a thin film of an evaporation retarding agent upon a water surface, and a composition which when added to water results in such a film. A solid admixture of the particulate retarding agent, which is a saturated, aliphatic, interface-active hydrocarbon, and a water soluble filler material is applied to the water surface in the form of a compacted unitary solid such as a tablet. The filler material serves to separate the particles of the retarding agent so it spreads more quickly upon contact with the water. Suitable filler materials are usually so dense that the bulk density of the compacted solid is greater than one. To maintain the compacted solid on the surface of the water while the retarding agent spreads, my U.S. Pat. No. 3,531,239 teaches the use of a filler material capable of generating a gas upon contact with water. My patent also teaches that the gas bubbles generated will bring evaporation retarding agents to the surface to form a film even in cases where the tablet itself sinks. A suitable gas generating filler material is sodium bicarbonate and tartaric acid.
In general, the longer the chain length of the hydrocarbon, the more effective is the resulting monomolecular layer as an evaporation retardant, but the slower the layer spreads over the water surface. For example, the smallest chain length that can seriously be regarded as an effective evaporation retardant is C.sub.16. Even a hydrocarbon with a chain length of C.sub.18 spreads too slowly to be practical for many purposes when applied alone in the manner described in my above referenced patent, so it normally must be mixed with a C.sub.16 hydrocarbon to improve the spreadability.